Attention has been focused on the effective use of biomass energies in order to prevent global warming. In particular, those originating from vegetables in particular can make effectively the use of hydrocarbons converted from carbon dioxide by photosynthesis through the growth process of the vegetables and thus have a nature so-called carbon neutral, which does not lead to an increase in carbon dioxide in the atmosphere in view of the life cycle. Biomass fuel has had a high degree of expectation as an alternative energy to petroleum from the viewpoint of depletion of petroleum resources and inflating oil prices.
The use of biomass energy has been variously studied also in the field of fuels for transportation. For example, if a fuel originating from an animal or vegetable oil can be used as diesel fuel, the fuel is expected to take an effective role in carbon dioxide emission reduction because of its synergistic effect with the high energy efficiency of a diesel engine. Examples of generally known diesel fuels using animal or vegetable oils includes fatty acid methyl ester oils (abbreviated as “FAME”). The FAME is produced by ester-exchanging triglyceride, which is a general structure of an animal or vegetable oil, with methanol with the aid of the action of an alkali catalyst. Various studies have also been carried out so as to use the FAME not only for diesel fuel but also for aviation fuel, i.e., jet fuel. Aircrafts spent enormous amounts of fuel and have been affected largely by the recent inflating oil prices. Under these circumstances, much attention has been paid to biomass fuel as an important item taking a role not only as a measure for preventing global warming but also as fuel alternative to petroleum. Currently, the use of the FAME in the form of a mixture with a petroleum-based jet fuel has been carried out in some airline companies although on a trial basis.
However, it is necessary to dispose of glycerin produced as a by-product during the process of producing the FAME as described in Patent Literature 1 below. Costs and energies are also required to clean the resulting oil.
Furthermore, the FAME has concerns about its low temperature performances and oxidation stability. Since aviation fuels in particular are exposed to extremely low temperatures during flight at high altitudes, they are required to satisfy highly strict low temperature performance standards. When the FAME is to be used, it is very much a situation that the FAME must be blended with petroleum-based jet fuel and the amount of the FAME must be small. For oxidation stability, the specification of aviation fuel has established the addition of antioxidants. However, when consideration is given to the stability of the base oil, the amount thereof must be small as well as for low temperature performance.